1. Field of the Invention
The present invention relates generally to polymer materials, and more specifically to a high strength polyethylene (HS-PE) fiber with a tensile strength ranging from 10 to 50 g/d obtained by a preparation method of melt spinning.
2. Description of Related Art
The high strength polyethylene fiber is a well known synthetic fiber with high strength and high elastic modulus, produced from ultrahigh molecular weight polyethylene (UHMWPE) with a molecular weight higher than 1,000,000. Right now, HS-PE fibers, Aramid fibers, and carbon fibers are considered three high performance fibers in the world. Due to its high strength, high modulus and low density, the UHMWPE fiber plays an important role not only in modern warfare, defense equipment and aerospace field, but also in civil fields. The HS-PE fiber is mostly produced by the melt spinning method and the gel spinning ultra-drawing method.
Chinese patent No. CN1539033 discloses an HS-PE fiber with a tensile strength higher than 15 cN/dtex, which is produced by a melt spinning process employing a polyethylene with a weight-average molecular weight lower than 300,000 and a ratio of the weight-average molecular weight to number-average molecular weight (Mw/Mn) less than 4.0 as the starting material. Because of the hyperviscosity, the melt has low fluidity, which makes it difficult to spin and to realize industrial production.
Since late 1970's, the gel spinning ultra-drawing method has been adopted by DSM Company (Netherlands) to realize the industrial production of UHMWPE. In this method, the UHMWPE is resolved by a solvent to relieve flexible polyethylene chain molecules from severe entanglement by the dilution effect. The precursor solution is then extruded from a spinneret hole and quenched to be phase-separated, and new-born gel precursor fibers with folded lamellar crystals and tie-molecule network are obtained. After solvent removing and ultra-after-drawing, final HS-PE fibers with linear chain structure are obtained.
Netherlandish patent NL 7900990 and U.S. Pat. No. 4,344,908 disclose the preparation method of a linear chain structure HS-PE fiber with a tensile strength higher than 35 g/d adopting decalin as a solvent. The spinning solution is prepared by dissolving UHMWPE in decalin. After extruding the precursor solution from a spinneret hole and quenching in air or cold water, new-born gel precursor fibers are obtained. Final HS-PE fibers with a linear chain structure are then obtained by solvent removing and ultra-heat-drawing.
European patents EP0064167 and EP0205960 and U.S. Pat. No. 4,455,273 disclose preparation methods of linear chain structure HS-PE fibers. The spinning solution is prepared by dissolving UHMWPE in a kerosene or white solvent. After a gel spinning process, extracting, drying and ultra heat-drawing, final HS-PE fibers with a linear chain structure are obtained.
Prior art melt spinning methods for preparing UHMWPE fibers employ UHMWPE as the only raw material, the melt of which causes unfavorable low fluidity. To solve this problem, flow modifiers or diluents as well as a spinning process under ultrahigh pressure are introduced to improve the fluidity, which make industrialization difficult. However, because of the lower orientation of crystallization resulted from the great number of entanglement points of the melt polyethylene chain molecules, HS-PE fibers can be hardly obtained when only PE with low molecular weight is employed.
No published literature on preparing HS-PE fibers with a tensile strength ranging from 10 to 50 g/d and tensile elastic modulus ranging from 400 to 2000 g/d based on the blend-melt-spinning process was found during a prior art search.